Here’s my explanation. Upper Red Lake has about 50,000 acres open to the public (and another 70,000 acres that get very little pressure as previously posted). Even if you think about the hundreds (or more realistically thousands) of houses on red lake, it’s still a MUCH lower ratio of houses / fishable acres compared to many other lakes.
As a basis for comparison, most metro lakes are 100-500 acres and have a couple dozen to a couple hundred houses on the lake.
Lastly, Red seems to get fairly light pressure in the spring, summer, and fall (at least from what I’ve seen when I’m up there).